| | Green or non-green | Method/source of ZnO NPs | XRD (ZnO crystal analysis) | Ref |
| | Nongreen | Ion exchange with zeolite | Crystalline peaks at 2θ = 4°–70° range of sharp intensity. The structure found is hexagonal wurtzite. | [1] | | Hydrothermal | Crystalline peaks at 2θ = 31.52°, 34.15°, 35.95°, 47.28°, 56.28°, 62.52°, 66.11°, 67.68°, 68.83°, 72.22°, and 76.84°. Hexagonal structure with different crystal planes, (100), (002), (101), (102), (110), (103), (112), and (201). | [37] | | Commercial (Systerm Chempur) | Crystalline peaks at 2θ = 31.98°, 34.63°, 36.46°, 47.69°, and 56.73°. Corresponds to hexagonal wurtzite structure. | [39] | | Commercial (NanoSany, Iran) | Crystalline peaks at 2θ = 30°–80° range of sharp intensity. Size of NPs = 58 nm. | [40] | | Green | Synthesized with essential oil of eucalyptus globulus | Crystalline peaks at 2θ = 31.74°, 34.38°, 36.21°, 47.49°, 56.54°, 62.86°, 66.43°, 67.89°, 68.99°, 72.76°, and 76.94°. Hexagonal structure with different crystal planes, (100), (002), (101), (102), (110), (103), (200), (112), (201), (004), and (202) with lattice constants a = b = 3.2578 Å, c = 5.2179 Å. Size of NPs = 24 nm. | [12, 41] | | Synthesized with palm olein | Crystalline peaks at 2θ = 30°–70° range. Hexagonal wurtzite structure with different crystal planes, (100), (002), (101), (102), (110), (103), (200), (112), (201). Referred to standard value of JCPDS No. 36-1451. | [32] | | Synthesized with citrus maxima (Pomelo) juice | Crystalline peaks at 2θ = 30°–80° range. Hexagonal wurtzite structure with different crystal planes, (100), (002), (101), (102), (110), (103), (200), (112), (201), (004), (202). Referred to standard value of JCPDS No. 36-1451. Crystalline size: 15–35 nm. | [35] | | Synthesized with Aegle marmelos | Crystalline peaks at 2θ = 30°–80° range with high and sharp intensities. Hexagonal wurtzite structure with crystal planes (100), (002), and (101) of lattice constants a = b = 3.2417 Å, c = 5.1876 Å. Size of crystals: 20 nm | [17] |
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